Booting a PC from a Vinyl Record

Summary

Most PCs tend to boot from a primary media storage, be it a hard disk drive, or a solid-state drive, perhaps from a network, or – if all else fails – the USB stick or the boot DVD comes to the rescue… Fun, eh? Boring! Why don’t we try to boot from a record player for a change? 64 512 byte DOS boot disk on a 10″ record, total playing time 06:10 on 45 rpm Update February 2022: Click here to observe the very same vinyl ramdisk booted on an IBM PCjr! So this nutty little experiment connects a PC, or an IBM PC to be exact, directly onto a record player through an amplifier. I made a small ROM on-chip boot loader that operates the built-in “cassette interface” of the PC (that was hardly ever used), which will now be invoked by the BIOS if all the other boot options fail, i.e. floppy disk and the hard drive. The turntable spins an analog recording of a small bootable read-only RAM drive, which is 64K in size. This contains a FreeDOS kernel, modified by me to cram it into the memory constraint, a micro variant of COMMAND.COM and a patched version of INTERLNK, that allows file transfer through a printer cable, modified to be runnable on FreeDOS. The bootloader reads the disk image from the audio recording through the cassette modem, loads it to memory and boots the system on it. Simple huh? The vinyl loader code, in a ROM (It can also reside on a hard drive or a floppy, but that’d be cheating) And now to get more technical: this is basically a merge between BootLPT/86 and 5150CAXX, minus the printer port support. It also resides in a ROM, in the BIOS expansion socket, but it does not have to. The connecting cable between the PC and the record player amplifier is the same as with 5150CAXX, just without the line-in (PC data out) jack. The “cassette interface” itself is just PC speaker timer channel 2 for the output, and 8255A-5 PPI port C channel 4 (PC4, I/O port 62h bit 4) for the input. BIOS INT 15h routines are used for software (de)modulation. The boot image is the same 64...